diff --git a/sofort/cfgtest.sh b/sofort/cfgtest.sh
index cb1e069..77ce1ea 100644
--- a/sofort/cfgtest.sh
+++ b/sofort/cfgtest.sh
@@ -146,6 +146,12 @@ cfgtest_interface_presence()
                 > /dev/null 2>/dev/null                   \
 	|| return 1
 
+	mb_internal_str=$(printf '%s%s' '-DHAVE_' "$@"  \
+			| sed -e 's/\./_/g'             \
+			| tr "[:lower:]" "[:upper:]")
+
+	cfgtest_cflags_append "$mb_internal_str"
+
 	return 0
 }